Stimulus-responsive polymeric particle formulations

Abstract

A stimulus-responsive formulation of stimulus-responsive polymer particles in aqueous composition has a rheology-stimulus profile (e.g. rheology-temperature) whereby it exhibits certain rheological behaviours over a range of temperatures, which is controllable by copolymerising a stimulus-responsive polymer-forming monomer, such as N-isopropylacrylamide, with a certain proportion of second monomer having weak acid functionality (such as acrylic acid) to form the stimulus-responsive microgel particles of the formulation and by addition of a base to the formulation to neutralise a portion but not all of the weak acid functionality. Thus a stimulus-responsive formulation may be controlled to exhibit gel-to-liquid-to-gel like behaviour with increasing temperature.

1 . A stimulus-responsive formulation comprising an aqueous dispersion or suspension of discrete stimulus-responsive crosslinked polymeric particles in aqueous medium, the polymeric particles comprising a co-polymer of at least a first stimulus-responsive polymer-forming monomer and a second polymer-forming monomer having a weak acid functionality, the formulation further comprising an acid-neutralizing agent or pH adjustment agent in an amount to neutralize a portion of the weak acid functionality of the polymeric particles. 
     
     
         2 . A formulation as claimed in  claim 1 , wherein the stimulus is a change in temperature. 
     
     
         3 . A formulation as claimed in  claim 2 , which comprises one or more of a concentration of polymeric particles dispersed in the formulation, a proportion of second polymer-forming monomer in the polymeric particles, and a concentration of acid-neutralizing agent or pH adjustment agent or a proportion of acid functionality neutralized selected such that the formulation demonstrates a desired rheology-stimulus profile. 
     
     
         4 . A formulation as claimed in  claim 3 , which is temperature responsive, wherein the proportions are selected such that the formulation demonstrates a desired rheology-temperature profile. 
     
     
         5 . A formulation as claimed in  claim 4 , wherein the desired rheology-temperature profile comprises a first thermal range in which the formulation has a first rheological profile or behavior, and either or both of a second thermal range and third thermal range, wherein the second thermal range is at higher temperature than the first thermal range and separated therefrom by a first transition point or first transition range and in which second thermal range the formulation has a second rheological profile or behavior, and wherein the third thermal range is at lower temperature than the first thermal range and separated therefrom by a second transition point or second transition range and in which third thermal range the formulation has a third rheological profile or behavior. 
     
     
         6 . A formulation as claimed in  claim 5 , wherein the desired rheology-temperature profile comprises a first, second and third thermal range. 
     
     
         7 . A formulation as claimed in  claim 6 , wherein the first thermal range is characterized by a rheological behavior that demonstrates liquid-like behavior, the second thermal range is characterized by a rheological behavior that demonstrates gel-like behavior and the third thermal range is characterized by a rheological behavior that demonstrates gel-like behavior. 
     
     
         8 . A formulation as claimed in  claim 1 , which comprises the polymeric particles in a concentration in the range 1 weight % to 10 weight %. 
     
     
         9 . A formulation as claimed in  claim 1 , wherein the second polymer-forming monomer is provided in an amount of 0.5 to 20 mol % of the total amount of monomer. 
     
     
         10 . A formulation as claimed in  claim 1 , wherein the acid neutralizing agent is provided at a concentration to ionize from 50% to 90% of the weak acid functionality. 
     
     
         11 . (canceled) 
     
     
         11 . A formulation as claimed in  claim 5 , wherein the polymer particles are in a collapsed state in the first thermal range and in a swollen state in the second thermal range and wherein the diameter of the particles in the collapsed state is greater than 80 nm. 
     
     
         12 . A formulation as claimed in  claim 1 , wherein the first stimulus-responsive polymer-forming monomer is selected from one or more of: N-alkylacrylamides, such as N-ethyl-acrylamide and N-isopropylacrylamide; N-alkyl-methacrylamides, such as N-ethyl-methacrylamide and N-isopropyl-methacrylamide; vinylcaprolactam; vinyl methylethers; partially-substituted vinylalcohols; ethylene oxide-modified benzamide; N-acryloylpyrrolidone; N-acryloylpiperidin; N-vinylisobutyramide; hydroxyalkylacrylates, such as hydroxyethylacrylate; and hydroxyalkylmethacrylates, such as hydroxyethyl-methacrylate. 
     
     
         13 . A formulation as claimed in  claim 12 , wherein the first stimulus-responsive polymer-forming monomer is N-isopropylacrylamide. 
     
     
         14 . A formulation as claimed in  claim 1 , wherein the second polymer-forming monomer is selected from substituted or unsubstituted alkanoic acids or alkenoic acids. 
     
     
         15 . A formulation as claimed in  claim 1 , wherein the second polymer-forming monomer is acrylic acid or methacrylic acid. 
     
     
         16 . A formulation as claimed in  claim 1 , wherein the polymeric particle comprises a random copolymer of N-ispropylacrylamide and acrylic acid. 
     
     
         17 . A formulation as claimed in  claim 1 , which further comprises a functional material. 
     
     
         18 . A formulation as claimed in  claim 17 , wherein the functional material is selected from a biologically active material, a colorant, a treatment agent, a fertilizing agent or crop treatment agent. 
     
     
         19 . A formulation as claimed in  claim 18 , wherein the functional material is a biologically active material and the formulation is for controlled delivery of a biologically active material. 
     
     
         20 . A formulation as claimed in  claim 19 , wherein the functional material is a colorant and the formulation is a printing ink. 
     
     
         22 - 31 . (canceled)